Possibility to physically reserve space without writing leaf blocks

*** 808,817 ****
--- 808,839 ----
          dnode_rele(dn, FTAG);
          return (err);
  }
  
  void
+ dmu_write_zero(objset_t *os, uint64_t object, uint64_t offset, uint64_t size, dmu_tx_t *tx)
+ {
+         dmu_buf_t       **dbp;
+         int             numbufs, i;
+ 
+         VERIFY(0 == dmu_buf_hold_array(os, object, offset, size,
+             FALSE, FTAG, &numbufs, &dbp));
+ 
+         for (i = 0; i < numbufs; i++) {
+                 dmu_buf_t *db = dbp[i];
+ 
+                 dmu_buf_will_zero_fill(db, tx);
+ 
+                 memset(db->db_data, 0, db->db_size);
+ 
+                 dmu_buf_fill_done(db, tx);
+         }
+ 
+         dmu_buf_rele_array(dbp, numbufs, FTAG);
+ }
+ 
+ void
  dmu_write(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
      const void *buf, dmu_tx_t *tx)
  {
          dmu_buf_t **dbp;
          int numbufs, i;
*** 1794,1803 ****
--- 1816,1826 ----
          zp->zp_level = level;
          zp->zp_copies = MIN(copies, spa_max_replication(os->os_spa));
          zp->zp_dedup = dedup;
          zp->zp_dedup_verify = dedup && dedup_verify;
          zp->zp_nopwrite = nopwrite;
+         zp->zp_zero_write = B_FALSE;
  }
  
  int
  dmu_offset_next(objset_t *os, uint64_t object, boolean_t hole, uint64_t *off)
  {